With the advent of increased fuel economy and reduced emissions requirements imposed by the government, various fuel systems have been developed to precisely control the amount of fuel that is injected during the injection events of a combustion cycle. In particular, high pressure fuel injection systems have been developed which provide increased control of the fuel injected by the fuel injectors of an internal combustion engine in comparison to conventional fuel injection systems.
Such high pressure fuel injection systems typically utilize at least one high pressure pump that pressurizes the fuel to be injected by the fuel injectors. Fuel systems may utilize a plurality of such high pressure pumps corresponding to the number of fuel injectors, each of the pumps providing highly pressurized fuel to a fuel injector. Other fuel systems utilize fewer high pressure pumps in conjunction with a high pressure common rail. The high pressure common rail may include a common rail fuel apparatus such as a high pressure accumulator. In an exemplary design, one or more high pressure pumps are connected to the high pressure common rail to thereby provide highly pressurized fuel to the fuel injectors of the internal combustion engine. The common rail then distributes the pressurized fuel to each of the fuel injectors.
Some high pressure fuel injection systems utilizes a hydro mechanical actuator to precisely control the quantity of fuel to be admitted to the high pressure fuel pump. In FIG. 1, for example, a conventional high pressure fuel pump system 10 is illustrated. A fuel supply 12 is dispersed in a supply line 14 such as via a low pressure fuel transfer pump (not shown). A hydro mechanical actuator 16 is configured to control the quantity of fuel 12 dispersed towards one or more high pressure fuel pumps 30. The fuel pumps 30 can include a high pressure piston pump suitable for dispersing fuel from a fuel supply 12 to a receptacle such as a common rail fuel apparatus or accumulator 42. An air bleed orifice 18 is provided to disperse air from within the supply, line 14 upstream to the hydro mechanical actuator 16. The hydro mechanical actuator 16 may include an inlet metering valve (IMV) having a variable area orifice operated, for example, by a solenoid. Thus, the IMV can include a variable area sleeve type valve that uses linear position to control the amount of fuel to be pumped through the supply line 14 towards one or more fuel pumps 30. Hence, the IMV is configured such that it may be actuated to a fully closed position in order to prevent fuel from passing downstream to the fuel pump 30. However, by nature of the sleeve type valve design, there may be a natural leakage rate that passes through the clearance of the sleeve valve.
A design of the conventional high pressure fuel pump system 10 shown in FIG. 1 includes inlet check valves 26 which allow fuel to be fed to one or more fuel pumps 30 via supply lines 28. The inlet check valves 26 are configured to open after a pressure buildup within the inlet check valve passage 17. This tolerance pressure may occur, for example, at 7 psi. Thus, when the pressure buildup exceeds 7 psi, the inlet check valve 26 opens to allow a flow of fuel to pass therethrough. The aforementioned pressure buildup may occur prematurely due to any fuel flow leakage from the IMV 16. The pressure buildup in the inlet check valve passage 17 can occur downstream to the IMV 16. Thus, once the tolerance pressure, for example, 7 psi, is achieved, the inlet check valve 26 is opened to allow fuel to be fed to fuel pump 30.
The exemplary embodiment of FIG. 1 illustrates a plurality of high pressure fuel pumps 30 which are driven via cams 32 and followers 34 in order to drive fuel towards outlet check valves 38 via supply lines 36. Again, the outlet check valves 38 are also configured to open, upon achieving a tolerance pressure, in order to allow fuel to pass therethrough towards the common rail fuel apparatus or high pressure accumulator 42. Upon obtaining the tolerance pressure, the outlet check valves 38 open and allow fuel to pass therethrough to be received by the accumulator 42 via supply lines 40.
Hence, under ideal circumstances, the fuel is precisely regulated from the fuel supply 12 via the IMV 16. This would, in turn, regulate an amount of fuel delivered to one or more fuel pumps 30. However, due to leakage of fuel past the IMV 16 into the inlet check valve passage 17 downstream to the IMV 16, the additional amount of fuel flow leakage can pressurize the system. The IMV 16 fuel leakage rate may be measured at approximately 5-40 cc/min. The presence of this additional fuel leakage within the high pressure fuel pump system 10 can produce additional pressurization downstream to the IMV 16 such as within in the inlet check valve passage 17 and at one or more inlet check valves 26. The increased pressurization can be sufficient to achieve the minimum tolerance pressure of the inlet check valves 26 and cause them to open. This will allow additional fuel to flow to one or more fuel pumps 30. Upon operation, the receipt of the aforementioned additional leakage of fuel flow received by one or more fuel pumps 30 will increase the pressure in supply lines 36 toward one or more outlet check valves 38. This additional pressurization created in supply lines 36 can achieve the minimum tolerance pressure of valves 38 required for opening and upon doing so will therefore allow additional fuel to flow towards accumulator 42. This additional amount of fuel can over-pressurize the accumulator 42 thus creating potentially negative effects.
In one example, a diesel engine may be equipped with the conventional high pressure fuel pump system 10 of FIG. 1. When the diesel engine is motored down, such as upon encountering long mountain grades, with a closed throttle pedal, the IMV 16 is commanded fully closed to prevent fuel from entering the fuel pump 30. However, the before mentioned leakage of fuel flowing past the IMV sleeve valve may be admitted to the fuel pump 30 where it is pressurized and delivered to the high pressure accumulator 42. The flow of fuel into the accumulator 42 during closed throttle engine motoring is undesired and causes the accumulator pressure to rise above the target pressure.
When the target pressure of the accumulator is exceeded, several undesirable effects may occur. For example, upon reopening the IMV 16, such as via the throttle pedal, an undesirable combustion noise may occur due to a fuel injection event occurring at higher pressures. Increased pressure may negatively affect components such as by reducing the service life of engine seals or causing other engine components to fail. Such failures may include creating fractures in fuel system components including, for example, fuel injector bodies.
Embodiments of accumulators 42 having pressure safety relief valves may also be affected. For example, undesirable increased pressure, as described herein, may trigger a relief valve to open in order to prevent the system from buildup of excessive pressure. However, continuous multiple and repetitive relief valve opening events, such as those occurring subsequent to encountering long mountain grades, occurring during unexpected openings as a result of fuel leakage from the IMV, can reduce the service life of the relief valve. This can induce increased costs for repair and possibly incur additional damages to the accumulator itself if the relief valve fails prematurely before being noticed. Damage to the accumulator could also adversely affect other components of the vehicle including creating additional damages.
Turning again to FIG. 1, a fuel drain supply line 22 is fluidly connected to fuel pump drain 44 of fuel drain circuit 20. The fuel drain supply line 22 receives fuel from one or more high pressure pumps 30. In some instances, the one or more fuel pumps 30 can operate even when the IMV 16 is in a closed position. Such operation may draw fuel from the fuel drain supply line 22 and pressurize the aforementioned fuel, for example, as the cam 32 enacts the piston of the piston fuel pump 30 in a stroke motion. This, too, can cause over-pressurization of the fuel pump system 10 including over-pressurizing components such as accumulator 42.
Thus, there exists a need to prevent undesirable pressure buildup within the high pressure fuel injection system and to address, at least, the aforementioned problems of the prior art.
The present disclosure is directed towards overcoming one or more shortcomings set forth above.